Functional layers implementation

[mjnagel]

We previously accepted an ADR to begin publishing functional layers of UDS Core. We now need to do the technical implementation.

At a high level the steps should include:

• Creating new packages/ folders and zarf.yamls for each functional layer identified in the ADR
• Modifying CI to drop the single-pkg-tests in favor of "single layer" tests (each layer should be tested with the base layer)
• Updating documentation to identify any dependencies between layers (i.e. monitoring depends on identity)
• Publishing workflows updated to publish each layer, using monolithic versioning (all versioned with core itself)
• Updating pepr/operator code to properly handle reconciliation when layers are not present. Also ideally create warning events when a Package CR contains configuration that is incompatible with the currently deployed layers.

Note that an initial draft of changes was created in #665, but needs completion primarily with the operator code and publishing.

[mjnagel]

If we want to keep the scope of the initial PR small, it is acceptable to just start with base + identity layers. We will need to track the other layers as follow-on work.